Measure soil tension or how forcefully water is being pulled out of the sensor into the soil. These metal meters tell you how hard your plant roots are workin to draw adequate water. The unit of measure used is centibars (cb). The higher the reading is in cb, the drier your soil. Model "R" for general use with row, tree and field crops. An easy-to-read dial displays soil moisture level, from 0 to 100. Using 2-3 different depths at each monitoring station gives you a complete picture of water movement and location in your soils. Service Kit (Item No. RIR1001, sold separately) is required for setup and maintenance of meter. USA made.